*{
    box-sizing: border-box;
    padding: 0;
}
html{
    height: 100%;
}
body{
    height: 100%;
}
footer{
    width: 100%;
    position: fixed;
    bottom: 0;
    left: 0;
    height: 60px;
    line-height: 60px;
    border-top: 1px solid gray;
}
footer span{
    float: left;
    width: 33.3%;
    border-right: 1px solid gray;
    text-align: center;
}
footer span:nth-child(3){
    border-right: none;
}

.active{
    background-color: lightblue;
}

ul>li{
    list-style: none;
}
div>header{
    text-align: center;
    height: 60px;
    line-height: 60px;
    font-size: 30px;
    
}

.chat ul li{
    /*   竖直对齐   */
    vertical-align: middle;
}
.chat ul li img{
    width: 50px;
    height: 50px;
    border-radius: 50%;
}
